Ironworkers and structural assembly persons have long recognized the need for an intersecting structural member that allows some degree of flexibility in assembly, while reducing the additional time spent securing the structural members created by the desired flexibility in assembly. Such long-felt needs have been particularly prevalent in the fields of ship and aircraft construction.
Many structures, such as those identified above, are constructed of a relatively thin skin material supported by underlying structural members that intersect in some combination of angles. An optimal design would allow for bonding of the structure's skin continuously along one edge of all the underlying structural members, and would allow all of the structural members to run continuously, that is, to not be interrupted at the points where the members intersect. However, a problem is created at each intersection of these structural members. The members generally intersect in one of three ways. Either the members must overlap, one member must pass through an aperture in the other, or one member must be discontinuous, that is, it must be interrupted and be joined to the sides of the other member. Numerous attempts have been aimed at improving the joints created by the intersection of these members.
The first method, that of overlapping intersecting structural members, is taught in U.S. Pat. No. 4,214,332 to Stoner. In the '332 method, continuous cross members are laid on top of continuous longitudinal members, and the members are fastened at each intersection. Such a technique allows for easy assembly, as there is a relatively large tolerance allowable in selecting the joining points. The technique also allows for the strength of two uninterrupted structural members, but prevents the skin of the structure from lying tightly against both members, as the members do not lie in the same plane. As the structural members are not coplanar, the structure's skin may be fastened to only one set of structural members. In the '332 patent, teaching a method of building a boat, the structural members run approximately longitudinally and transversely in the boat hull, and the skin is fastened to the longitudinal members. Accordingly, a gap is produced between the vessel's skin and all of the transverse members.
The second method of intersecting structural members involves passing one structural member through an aperture in another structural member in a generally notching method of assembly, and can be seen to fall into two general classes; tight and non-tight joining.
Tight joining may be defined as that where the aperture (notch) and the member to fit within it are extremely close to one another in shape and size, so that the structural members fit somewhat tightly together, and the fastening of the two, by such means as adhesives, soldering, brazing, or welding, essentially closes any gap between the structural members to be joined. Tight joining has the advantage of it being relatively easy to close the gap between the structural members, as the gap is small and the fastening method substantially or completely closes the gap. Because the gap between structural members is filled by the bonding material, connections between the structural members are intrinsically waterproof, or nearly so. It has the disadvantage of requiring very close manufacturing and assembly tolerances, and careful craftsmanship in assembly, all of which increase costs and complexity, and are especially difficult to achieve in shipbuilding or other applications where large components are being fabricated.
Non-tight joining may be defined as that where the aperture and the member to fit within it are considerably different in shape and size, that is, the member being considerably smaller than the aperture, so that the intersecting structural members fit only loosely together when they are assembled. This loose fit makes it relatively difficult to close the gap between the structural members, and an additional piece or pieces, called a collar, is traditionally fixed around the aperture to secure the members and close the gap. Non-tight joining has the advantage of being relatively easy to assemble, as there are large tolerances allowable in the fit between the members.
It has the disadvantage of requiring a third (and sometimes more) piece, the collar, to secure the joint between the members. Securing structural members with collars requires a plurality of collars in typical construction, leading to increases in labor, weight, material costs, and complexity of assembly. Additionally, such collars need to be closely fitted to the gap between the members if the gap is to be effectively closed, as for example, in ship construction where a watertight intersection may be desired.
One method of tight joining is taught in U.S. Pat. No. 1,805,669 to Liamin. In the '669 patent, the transverse ribs of a metal boat are notched to accommodate continuously running longitudinal members. This allows both transverse and longitudinal members to run continuously, but creates exacting conditions for assembly, in that each structural intersection must be precisely aligned for assembly. Any error in alignment will not only cause a single joint to be misaligned, but the error will be transmitted and amplified along the run of the structural members, and will cause further misalignment.
The third method of intersecting structural members involves making only those members passing parallel to one another continuous, and then fastening intersecting structural members to the sides of the continuous members. This is exemplified in U.S. Pat. No. 1,821,882 to Curr. The '882 patent teaches longitudinal beams welded to the sides of continuous transverse webs. This construction has the advantage of relatively easy assembly and generous assembly tolerances. It has the disadvantage of decreased strength in certain applications when compared to the technique of having all structural members run continuously through intersecting joints. This is particularly true in military shipbuilding where continuous structural members increase the structure's ability to sustain highly dynamic loads.
What continues to be needed but missing from this field of art is a structure and method that combines the advantageous aspects of all of these methods of structural member intersection. An optimal solution would allow the enhanced strength seen when all structural members are continuous, as seen in the overlapping method and the tight and non-tight notching type methods of assembly. The optimal solution would further allow one edge of all structural members to be approximately coplanar, as seen in both the tight and non-tight notching systems, would allow for easy assembly with large tolerances in assembly like the non-tight assembly, and would produce relatively close gaps within the intersecting joint without the addition of collars, as with tight assembly.
The instant invention addresses many of the shortcomings of the prior art and allows for all the heretofore unavailable benefits. Two intersecting structural members are allowed to run continuously, without interruption at the joints where they meet. Because one member passes through another, one edge of each structural member can remain coplanar with an edge of the other structural member, and therefore both members may be fully bonded along one edge to the skin of the structure. The structural members are assembled with an increased ingress area, allowing for wide assembly tolerances, and the ingress area is then easily closed to accomplish a mating of the structural members. This removes the need for collars in non-tight applications. Eliminating the need for collars decreases the number of parts needed, decreases total assembly weight, decreases the amount of welding required, speeds assembly, and contributes excellent resistance to metal fatigue.